Details of the incident Friday in Afghanistan's northwestern Farah province have been sketchy and often contradictory. An Interior Ministry statement said 300 Afghan laborers tried to cross into Iran illegally, looking for work. Iranian border guards opened fire, killing 10, it said. The ministry also blamed its own border guards for allowing the laborers to cross, though they had neither visas nor passports. Two Afghan border guards were dismissed and could face charges of neglect of duty, the ministry said.

In Tehran, Iran's chief of border guards, Gen. Hamid Sharafi, denied there was any shooting at Afghan migrants, according to Iran's semi-official ISNA news agency.

"Such a report is not right. We do not confirm it based on our investigations," Sharafi said.

Several wounded laborers who arrived at the Farah district hospital for treatment also reported dead compatriots and said as many as 21 laborers were taken away by the Iranian border guards, said Abdul Rahman Zhawandai, a spokesman for the Farah provincial governor.

On Saturday, Afghan Foreign Minister Zalmai Rasoul called the Iranian ambassador to Afghanistan to lodge a complaint and to seek more details about the incident, said Foreign Ministry spokesman Janan Mosazai.

"We are following this issue very seriously through our embassy in Tehran," Mosazai told reporters Sunday. While admitting that the migrants were trying to enter Iran illegally, he said "the reaction of Iran should have been a civilian reaction, not a military" one — a reference to the shooting.

Protests over the incident erupted on Sunday on the Afghan side of the border. Dozens of residents demonstrated in the streets of the provincial capital, also named Farah, shouting anti-Iran slogans.

Poor Afghans often try to sneak into Iran in search of work as day laborers.

Elsewhere in Afghanistan, a roadside bomb on Sunday killed a district prosecutor in southern Helmand province, where Taliban insurgents roam with relative ease in much of the countryside.

The bomb struck early in the morning as prosecutor Mohammed Lal Hakimi was on his way to work, said Ummar Zawaq, a spokesman for the provincial governor.

Zawaq said the district prosecutor received threats from the Taliban, angry about the number of insurgents he convicted and sent to prison.

No one claimed responsibility for the killing, but Taliban have stepped up their assassinations in recent months, attacking government and security officials they accuse of being traitors.